1. Field of the Invention
This invention relates to a method for producing a nuclear halogenated aromatic compound possessing cyano groups by causing a gas containing an aromatic compound possessing cyano groups to react with a halogen gas in the gaseous phase.
2. Description of the Prior Art
As methods for the production of nuclear halogenated aromatic compounds possessing cyano groups, methods for the production of tetrachloroorthophthalonitrile, for example, have been already known.
Saito et al., for example, disclose a method for producing tetrachlorophthalonitrile by the reaction oforthophthalonitrile with chlorine gas in gas phase in the presence of activated carbon as a catalyst in "Journal of Organic Synthetic Chemistry Society", Vol.22, page 834 (1964). This report, however, fails to clarify the problems which arise in the commercialization of the method and, therefore, does not offer any definite measure for the solution of these problems. JP-B-50-38,089 and JP-B-63-65,065 also disclose similar methods. The methods which are disclosed specifically therein, however, are those for the production of tetrachloroisophthalonitrile. Similarly to the report regarding tetrachloroorthophthalonitrile, these patent publications do not clarify the problems which arise in the commercialization of the methods. Thus, no specific measure has been proposed for the solution of those problems which arise in the commercialization of nuclear halogenated aromatic compounds possessing a nitrile group.
Concerning the method for producing a nuclear chlorinated aromatic compound by the reaction of a gas containing an aromatic compound possessing cyano groups with chlorine gas in the gaseous phase, it is reported in "Journal of Organic Synthetic Chemistry Society, " Vol. 22, pages 743 -748 and ibid, pages 834-837 that activated carbon functions as an excellent catalyst possessing the activity of forming tetrachlorophthalonitrile in gas-phase catalytic chlorination of phthalonitrile. JP-B-44-29, 853 has a mention to the effect that in the gaseous-phase catalytic chlorination of benzonitrile, activated carbon, for example, is capable of augmenting the production velocity of pentachlorobenzonitrile, also lowering the reaction temperature, and fulfilling an important role in precluding the decomposition of the nitrile group by chlorination which is liable to occur at elevated temperatures. The technical literature and the patent publications mentioned above have absolutely no description of the improvement of the service life of activated carbon as a catalyst and have not taken up this matter as a subject for study. Barely, "Journal of Organic Synthetic Chemistry Society" carries in Vol. 22, pages 834-837 thereof a report to the effect that the activity of activated carbon manifested in catalyzing the formation of tetrachlorophthalonitrile shows no sign of decline even after about 110 hours' use.
As respects the improvement of the service life of activated carbon as a catalyst, we have already published in "Journal of Organic Synthetic Chemistry Society," Vol. 47, pages 20-26, a report to the effect that activated carbon, as the optimum catalyst for the reaction of chlorination of benzonitrile, manifests the highest activity and high selectivity and that the service life of the catalyst can be expected to be elongated in proportion as the pore volume of the catalyst is increased.
Our knowledge as of the time of this publication, however, is based on the results regarding such pore volumes as embrace even a region of very large pore radiuses on the theory that the requirement necessary for the elongation of the service life of activated carbon as a catalyst resides solely in the parameter regarding pore volume. It, therefore, lacks perfect repeatability and even incurs the possibility that the long service life normally expected will not be obtained when the kind of catalyst is changed. Further, the largest pore volume, 0.95 cc/g, that is possessed at all by any of the activated carbon reported therein is equal to that of the activated carbon used as a catalyst in Control 1 which will be specifically described herein below and the cumulative pore volume of the region of activated carbon possessing pore radiuses of 5-100 .ANG. as determined by the steam adsorption method is only air equivalent to 0.43 cc/g. Even when the activated carbon possessing the same pore volume of 0.95 cc/g as reported herein is adopted as a catalyst, therefore, the service life offered by this activated carbon never deserves to be called fully satisfactory. The desirability of further improving the activated carbon excelling in repeatability and enjoying a long service life as a catalyst has been finding widespread recognition for the sake of promoting commercialization. It may well be regarded as a task to be attained.
An object of this invention, therefore, is to provide a method for the production of a nuclear halogenated aromatic compound possessing cyano groups.
Another object of this invention is to provide a measure for the solution of the problems which arise in the production of a nuclear halogenated aromatic compound possessing cyano groups on a commercial scale.
The production of a nuclear halogenated aromatic compound possessing cyano groups by the reaction of a gas containing an aromatic compound possessing cyano groups with halogen gas in gas phase in the presence of a catalyst necessitates vaporization of a corresponding solid aromatic compound possessing cyano groups. The aromatic compound, before and after the vaporization, gives rise to various self-condensates of the aromatic compound possessing cyano groups. It has been found that these self-condensates entrain various problems such as clogging pipes, adhering to the catalyst so fast as to induce coalescence of catalyst particles and degradation of catalytic activity, or impairing the quality of the product. Still another object of this invention, therefore, is to provide a measure for the solution of these problems.
Yet another object of this invention is to provide, in the gas-phase catalytic halogenation of an aromatic compound possessing cyano groups, a method for the production of a nuclear halogenated aromatic compound possessing cyano groups by the use of activated carbon capable of retaining the activity to form the compound for a long time (long service life) and deserving high esteem as an excellent catalyst.